Anomphalus cf. vanescens Yochelson, 1956

Ketwetsuriya, Chatchalerm, Karapunar, Baran, Charoentitirat, Thasinee & Nützel, Al- Exander, 2020, Middle Permian (Roadian) gastropods from the Khao Khad Formation, Central Thailand: Implications for palaeogeography of the Indochina Terrane, Zootaxa 4766 (1), pp. 1-47 : 22-23

Anomphalus cf. vanescens Yochelson, 1956

( Fig. 17 A–E)

cf. Anomphalus vanescens Yochelson, 1956: 253 , pl. 22, figs 19–22; Pan & Yu, 1993: 46, pl. 9, fig. 3.

Material. Three specimens: ESKU-19- LP 30, 31, 50.

Dimensions (mm): ESKU-19- LP 30: height = 4.4; width = 7.7. ESKU-19- LP 31: height = c. 4.1; width = 6.7. ESKU-19- LP 50: height = 3.7; width = 5.5.

Description. Shell small, low-spired, rotelliform comprising about three whorls; whorls smooth, convex. embracing at periphery; whorls ornamented by numerous fine and dense prosocline collabral threads; upper whorl face somewhat flattened with convex periphery at mid-whorl; suture shallowly impressed, distinct; base flatly convex, narrowly phaneromphalous; umbilicus deep; aperture not certainly known.

Remarks. Anomphalus vanescens Yochelson, 1956 from the Permian of the Southwestern USA and from the Early Permian of China ( Pan & Yu 1993, p. 46, pl. 9, fig. 3) is similar but has a flatter spire, whorls embrace above periphery and whorls are lower. A. studiosus Yochelson, 1956 (p. 254, pl. 22, figs 25–28) is also similar in shell shape as well as the rate of whorl expansion but has smaller size, a narrower umbilicus has a flatter spire and its whorls embrace above periphery. A. fusuiensis Pan & Erwin, 2002 from the Late Permian of South China is also similar but has lower, more rounded whorls, a wider umbilicus and a deeper suture. The Middle Permian species A. lateumbilicatus Nützel & Ketwetsuriya, 2016 from the Tak Fa Limestone of Thailand has a very wide umbilicus and consists of more whorls compared to the A. cf. vanescens at comparable size. Anomphalus sp. which is reported from the Tak Fa Limestone is also similar but has a wider umbilicus and a flatter spire. Anomphalus sp. from the Permian of Malaysia as reported by Batten (1979, p. 8, figs 10–11) is higher spired. The present specimens also resemble A. japonicus Nützel in Nützel & Nakazawa, 2012 from the Middle Permian of Japan but the latter has a wider umbilicus and a small umbilical ridge. The present species is probably undescribed but the preservation of the material is too poor for a safe species assignment, especially the aperture and the collabral threads is hardly visible in the studied specimens.

Figures

FIGURE 17. A–E, Anomphalus cf. vanescens Yochelson, 1956, A–C, ESKU-19-LP 30. D–E, ESKU-19-LP 50. F–L, Anomphalus? blancus Kues & Batten, 2001, F–I, ESKU-19-LP 67. J–L, ESKU-19-LP 96. Scale bars represent: 2 mm (A–C); 1 mm (D–L).